smb/server: fix incorrect file size in get_file_compression_info()

smb/server: fix incorrect file size in get_file_compression_info()

Before this patch, we got the wrong file size:

  - client: touch /mnt/file
  - client: smbinfo setcompression default /mnt/file
  - client: dd if=/dev/zero of=/mnt/file bs=1 count=1000
  - client: smbinfo filecompressioninfo /mnt/file
            Compressed File Size: 4096
            Compression Format: 2 (LZNT1)

After this patch, we get the correct file size:

  - client: smbinfo filecompressioninfo /mnt/file
            Compressed File Size: 1000
            Compression Format: 2 (LZNT1)

Note that the actual compressed file size must be got by other methods.
For Btrfs, use the following command to get actual compressed file size:

  - server: compsize /export/file
            Processed 1 file, 0 regular extents (0 refs), 1 inline.
            Type       Perc     Disk Usage   Uncompressed Referenced
            TOTAL        4%       47B        1000B        1000B
            zlib         4%       47B        1000B        1000B

Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>